My brand new MacBook Pro with Lion doesn't detect my external Samsung SyncMaster. Following all the suggestions found here and elsewhere, including disconnecting and reconnecting, turning the power supply off and on again etc. does not work. However, if I connect the Mac to my Samsung TV it usually finds it and then I can take the pc back and connect it to my monitor again and it works.

Unfortunately, once the monitor goes into sleep mode for not being used for some minutes, the Mac does not detect it again, and I have to connect to the TV first and then the monitor again.

This is so annoying. I am thinking of buying af new monitor - or maybe installing windows, that had no issues with this external screen.

You have to unplug the power cable from the syncmaster... then plug in the mini diplay adapter... then do a "detect display" is system preferences to check to see if it's detecting it... then simply close the lid to the laptop and plug in the power to the syncmaster... it will "detect" the monitor and it comes back every time for me now... I've dealt with this issue for over a year.... but it's how I get my external monitor back up every time. Apple and Samsung need to get together and fix this but until then it's the only thing that has worked for me...

I had the same problem described by others - my MacBook Pro stopped recognizing an external monitor. At first I dismissed the idea that my mini-display port to HDMI adapter might have suddenly stopped working. However, I replaced it and the problem is solved.

As I said the other day, I set up an LG screen and it worked well. At least, that's what I thought. Today it was almost impossible to get the external screen to show anything, because the MacBook has been in sleep mode running on batteries.

I tried about everything: Rebooting, switching off completely, removing and inserting the Thunderbolt->VGA adapter etc. The only thing that finally worked was the following: Shut down the Mac. Turn it on and close the lid. It will now boot up on the external screen. Now, before it comes to the login page, open the lid again and you should have the extended screen working beside the labtop's screen.

Well … SanctionOne's solution was working, for about 10 seconds, and then it crapped out on me again. I'm running an Acer V223W.

Same problems as many report. I initially used a Thunderbolt to DVI adapter but the MB Pro was locked up every morning, so I had to do a hard reboot to fix it (otherwise, it was nonresponsive, including unplugging the video adapter). I switched to a Thunderbolt to VGA adapter and that had worked fine for many months, until just yesterday. Unlike with the DVI adapter, I can recover using the VGA adapter. I've tried switching back and forth, unplugging the adapters, rebooting the Mac, detecting displays from the system pref, but nada. Very frustrating.

I have tried the wife's MB Air with the same VGA cord and Display Port adapter, and it drives the Acer monitor just fine.

I have replied a few months ago. My HP 23 LED monitor hooked to my MBP by a Thunderbolt-DVI adaptor does not consistently bootup with the MBP, never has.When it does not, the trick of unplugging the power plug on the monitor, then unplugging the adaptor from the MBP, waiting until the MBP screen flashes blue and resets, then quickly plugging in the monitor (it begins to scan for a signal) and then plugging in the adaptor to the MBP>gets the monitor up and going.

About half the time the monitor boots up on its own, but about half the time I need to use the above work-around.

From the other posts, I still can't believe their are that many funky adaptors and am still prone to believe that this is some SW problem with non-Apple monitors interfacing with the MBP.

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